I. Field of the Invention
The present invention is directed to an improvement in vehicle-mounted police radar warning receivers, and more particularly to such a receiver in which the intensity or volume of an audio alarm indicator, for example, may be automatically reduced after it is first energized during a police radar alarm condition.
II. Description of the Prior Art
Police radar may operate, for example, in the X-band and K-band of the frequency spectrum as discussed in U.S. Pat. No. 4,313,216, assigned to Cincinnati Microwave, Inc., the assignee herein. There are, generally, two types of police radar. One emits a continuous radar signal so long as the radar unit is turned on. The other emits a brief burst of radar signal when the police officer triggers the unit. This latter type is referred to as pulsed or instant-on radar. While transmitting, both continuous and pulsed radar transmit a signal which is generally at a fixed frequency within the selected band.
An electronic assembly referred to as a police radar warning receiver has been devised to detect the presence of police radar signals. An example is the PASSPORT radar warning receiver manufactured by the assignee herein, Cincinnati Microwave, Inc. of Cincinnati, Ohio. The police radar warning receiver is contained in a box-like housing which may be set on the dash or clipped to the visor of a vehicle, such as a passenger car or truck, motorcycle, boat or the like, which travels on land or water in areas subject to speed-monitoring radar surveillance by police. The front panel of the receiver faces the driver and has various indicators and control knobs. The receiver functions to detect the presence of the police radar and provide the driver or user with an audible and/or visual indication that his speed is being checked by radar.
The circuitry employed in the PASSPORT radar warning receiver to determine whether police radar signals are present is disclosed in aforementioned U.S. Pat. Nos. 4,313,216, and 4,581,769, which is also assigned to the assignee hereof.
When police radar is operating within range of the radar warning receiver, the driver is alerted by an alarm. For example, in the PASSPORT radar warning receiver, when a police radar alarm condition exists, i.e., when police radar is detected, a light is energized and an audible tone is generated. The audible tone is generated intermittently so as to sound like a series of beep tones or so-called "brap" tones, depending upon whether the received police radar signal is in the X- or K-band, respectively. The intensity or loudness of the beep or brap tones is determined by the setting of the volume adjust selected by the driver. However, the rate of beeping, i.e., the delay between each beep or brap tone, is inversely proportional to the strength of the received police radar such that the "beep rate" increases as the vehicle nears the source of police radar until the signal is so strong that the beeping or brapping tones will sound continuously.
The alarm in the PASSPORT radar warning receiver is energized for a minimum of about four seconds whenever a police radar signal is detected, so the driver will be alerted even when brief signals from pulsed radar are involved. Also, if the police officer triggers the unit within four seconds of the first trigger, the PASSPORT radar warning receiver's alarm will remain energized rather than terminate and sound a new warning. Similarly, with continuous radar, the alarm is energized for as long as the radar warning receiver can detect the radar signal plus the four additional seconds.
The radar warning receiver is sensitive enough to detect a police radar signal, even though the radar unit may be some distance away. As a result, the vehicle in which the radar warning receiver is mounted may travel quite a distance before the radar signal becomes too weak to detect. Hence, the alarms are likely to be energized for quite some time.
During prolonged alarm conditions, the alarms, especially the audible alarm, may tend to become an annoyance. Once the alarm is noticed, the driver may prefer to disable the audible alarm, for example, for the remaining time during which the alarm condition is present. To this end, the PASSPORT radar warning receiver is provided with a manual mute function. As described more fully in U.S. Pat. No. 4,631,542, also assigned to Cincinnati Microwave, Inc., the driver may manually cause termination of the alarm after the driver becomes aware of the alarm condition by physically depressing a momentary switch to terminate the alarm after becoming aware of the alarm condition. Under certain conditions, a driver may not be able to readily mute the audio alarm in this way, allowing the alarm to become an annoyance. Further, several separate alarm conditions may arise during the course of a long highway drive, for example. The driver may, thus, have to manually mute the audio alarm on several separate occasions.